smc: Introduce an id and prefix all log messages with SMC(ID)

When OpenBSC is handling more than one message at a time it is difficult
to see which log message belongs to which SMC. Introduce a uint64_t id
that can be set to the row_id/message_id and prefix all log messages
with SMC(ID).

This change is ABI and API incompatible with previous versions of
libosmogsm.

Example:
SMC(100) instance created
SMC(100) message MNSMS-EST-REQ received in state IDLE
2 files changed